Antibodies of the J606 murine VH family, GAC (group A- streptococcal carbohydrate) (GAC-related VH genes), have been seen to derive in normal mice from at least 3VH gene segments (of a locus whose complexity is 10-12). Two of these are GAC- related, one inulin related. In CBA/N mice, which do not respond to either GAC or inulin by conventional immunization methods, antibodies of the J606 VH family origin were found to constitute about 5% of their B cell VH pre-immune repertoire. The extent of expression of the members of the J606 VH family has been examined by nucleotide sequencing of hybridoma derived VH J606 genes from their purified mRNA.